Annual report pursuant to Section 13 and 15(d)

Equity - Schedule of Issued Shares of Class A common stock Under 2009 Long-Term Incentive Plan (Detail)

v3.6.0.2
Equity - Schedule of Issued Shares of Class A common stock Under 2009 Long-Term Incentive Plan (Detail) - 2009 Long-Term Incentive Plan [Member] - shares
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Schedule Of Employee Incentive Compensation Plans Disclosures [Line Items]      
Shares issued to employees upon exercise of stock options 1,032,174    
Class A Common Stock [Member] | Independent Directors Compensation Plan [Member]      
Schedule Of Employee Incentive Compensation Plans Disclosures [Line Items]      
Shares issued to independent directors for services rendered, in lieu of cash compensation 18,638 16,887 19,542
Class A Common Stock [Member] | Stock Option [Member]      
Schedule Of Employee Incentive Compensation Plans Disclosures [Line Items]      
Shares issued to employees upon exercise of stock options 19,060 33,825 354,926